this catapult will shoot a 1/2 inch marble 100 feet

Step 1: Frame

The base is a 2x2 foot square with two 3 foot uprights. The uprights are screwed into the inside of the box in the center of the frame.
<p>How did you make the hole for the metal rod?</p>
with a hole saw that goes on a drill
I bought them at Lowe's.
Where did you buy/find those springs
Please post questions if you have any.